Corrosion is a significant problem in petroleum refineries and other industrial plants which process corrosive materials. Corrosion can cause deterioration of valves, gauges and other equipment. Corrosion can also cause leaks with large environmental and financial costs.
Various sensors can be used to monitor corrosion. Typically a sensor will be connected to a display which can be monitored to determine the relative corrosion rate which has occurred to the pressure containment system. The most common areas of corrosion concern in the pressure containment boundary are at the interior wall of a pipe or vessel.
Alternatively, models can be used to predict the level of corrosion from known plant operating parameters. For example, predictive corrosion models exist for estimating corrosion levels from operating temperature, flow conditions and composition of the liquid inside the plant operating unit.
Based on either a sensor or a corrosion model, the plant operator can take action if the corrosion rate has reached an excessive level. For example, the operator might choose to reduce throughput, change process conditions, or shut down the process or use corrosion inhibiting chemicals.
Typically, corrosion sensors are fabricated out of a corroding material and corrosion is monitored by measuring the amount of corrosion or corrosion rate which has occurred on the sensor itself. However, one really wants to know how much corrosion has occurred on the equipment being monitored. For example, in the case of a pipe or reactor vessel, one might want to know how much corrosion or corrosion rate that has occurred on the wall of the pipe or reactor vessel.
Typically, corrosion sensors measure the relative amount of corrosion that has occurred. For example, a corrosion sensor might be able to determine that the corrosion rate has increased. However, it is even more preferable to know the absolute level of corrosion or corrosion rate that has occurred to a process unit—for example on a pipe wall.
The present invention is a method for determining the amount of corrosion which has occurred on the interior of a process unit from the amount of corrosion information which is measured on a sensor. As part of the methodology, this invention also devises a measurement protocol to relate the sensor output to its metal loss. Consequently, this invention provides the necessary method of calibrating the output of the corrosion sensor to metal loss on the process containment equipment such a pipes and vessels.